Utilisation des nanocelluloses pour des papiers sécurité

L’originalité de ce travail est d’étudier la contribution des nanocelluloses pour limiter deux défauts courant dans les papiers sécurités: le froissage et les “cornes”, où plis qui se manifestent dans les angles des papiers. Ces défauts sont principalement causés par une manipulation quotidienne de ces papiers à haute valeur ajoutée, et sont responsables d’une perte en qualité visuelle et mécanique ainsi que de troubles économiques. Les nanocellulose peuvent être divisées en deux différentes familles de matériaux : les nanofibrilles de celluloses (NFCs) et les nanocristaux de cellulose (NCCs). Les NFCs sont longues et flexibles et peuvent facilement s’enchevêtrer pour former un réseau cohésif maintenu par de nombreuses liaisons hydrogènes. Les NCCs sont des matériaux petits et rigides, et leurs impressionantes propriétés mécaniques font d’eux des candidats intéressants pour être utilisés en renfort de polymère. Dans cette étude, deux stratégies sont proposées pour incorporer ces deux types de nanocellulose dans la fabrication du papier sécurité. Premièrement, il est question d’introduire une couche de NFCs à l’intérieur du papier afin d’augmenter la résistance de ce papier au froissage. Ensuite, il est question d’imprégner ce papier avec de l’alcool polyvinylique renforcé par des NCCs afin d’augmenter la résistance aux cornes. Enfin, ces approches sont testées à l’échelle pilote et industrielle.The original feature of this work is the use of nanocellulose for limiting two security paper defects: corner folds, also called “dog-ears”, and crumpling. These defects, caused principally by daily handling of these high added value documents, are responsible for a decrease of paper visual and mechanical quality and constitute an economic loss. Nanocellulose can be divided into two different families: cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs). CNFs are long and flexible materials with the ability to entangle and form a network strongly maintained by hydrogen bonds. CNCs are short and rigid materials whose outstanding mechanical properties make them good candidates for reinforcement in a polymer matrix. In this study, two strategies are proposed to incorporate these two kinds of nanocellulose in the security paper process. First, it is question to introduce a CNF layer within the paper substrate in order to increase the paper crumpling resistance. Then, it is question to impregnate the paper with CNCs-reinforced polyvinyl alcohol (PVOH) in order to increase the dog-ears resistance. Finally, these approaches are tested at pilot and industrial scales

Hybrid nanopaper of cellulose nanofibrils and PET microfibers with high tear and crumpling resistance

International audienceCellulose nanofibrils (CNF), once filtered and dried, have the particularity to form a highly cohesive network, nanopaper. One of the drawbacks of all CNF nanopapers is their relative brittleness and low tear resistance, measured as the force needed for crack propagation after introducing a notch. In this work, hybrid nanopapers with drastically improved tear and crumpling resistance were produced by introducing polyethylene terephthalate (PET) microfibers into the CNF suspension prior to sheet fabrication. The PET microfibers were well dispersed in the CNF suspension and subsequently evenly distributed in the formed sheets. Incorporation of 10 wt% PET fibers increased the dry tear resistance with notch by a factor of 10 while still maintaining most of the mechanical properties. This effect is attributed to the loosely bound PET fibers which limit the crack propagation by dissipating the energy. It was also possible to improve the wet tear resistance by a factor of 4. Furthermore, incorporation of PET fibers allowed for crumpling of nanopaper that previously was so brittle it shattered from the deformation. Finally, incorporation of PET fibers also improved the crumpling resistance of wet samples. The improved wet properties, together with a higher and tunable porosity, open up the possibility to use these hybrid nanopaper sheets in filtration applications

Hybrid nanopaper of cellulose nanofibrils and PET microfibers with high tear and crumpling resistance

International audienceCellulose nanofibrils (CNF), once filtered and dried, have the particularity to form a highly cohesive network, nanopaper. One of the drawbacks of all CNF nanopapers is their relative brittleness and low tear resistance, measured as the force needed for crack propagation after introducing a notch. In this work, hybrid nanopapers with drastically improved tear and crumpling resistance were produced by introducing polyethylene terephthalate (PET) microfibers into the CNF suspension prior to sheet fabrication. The PET microfibers were well dispersed in the CNF suspension and subsequently evenly distributed in the formed sheets. Incorporation of 10 wt% PET fibers increased the dry tear resistance with notch by a factor of 10 while still maintaining most of the mechanical properties. This effect is attributed to the loosely bound PET fibers which limit the crack propagation by dissipating the energy. It was also possible to improve the wet tear resistance by a factor of 4. Furthermore, incorporation of PET fibers allowed for crumpling of nanopaper that previously was so brittle it shattered from the deformation. Finally, incorporation of PET fibers also improved the crumpling resistance of wet samples. The improved wet properties, together with a higher and tunable porosity, open up the possibility to use these hybrid nanopaper sheets in filtration applications

Impregnation of paper with cellulose nanocrystal reinforced polyvinyl alcohol: synergistic effect of infrared drying and CNC content on crystallinity

International audiencePaper was impregnated with neat polyvinyl alcohol (PVOH) or cellulose nanocrystal (CNC) reinforced PVOH, and dried by infrared radiation. Complex phenomena involved during paper impregnation and drying have been rarely investigated in the scientific literature, although these steps are crucial for the properties of the ensuing paper. The drying kinetics was studied and it showed that CNC tends to reduce the skin effect classically observed during fast PVOH drying. Furthermore, the nanoparticles induced faster water removal at the end of the drying step, which can be explained by an increase of the absorbed heat flux density. In addition, PVOH crystallization mechanisms have been studied through classical equations (Avrami, and Arrhenius) and a model (the Hoffman–Weeks method) and it was proved that both the drying conditions and the presence of CNC act on the crystallization of the polymer

Thick Polyvinyl Alcohol Films Reinforced with Cellulose Nanocrystals for Coating Applications

International audienceThe strain-induced elastic buckling instability for mechanical measurements (SIEBIMM) method was used to quantify Young’s modulus of polyvinyl alcohol (PVOH) coatings reinforced with cellulose nanocrystals (CNCs). The effect of processing parameters, namely, deposition method and drying temperature, and changes in relative humidity were assessed. The coatings were relatively thick (0.6–17.6 μm) compared to freestanding PVOH/CNC nanocomposite films tested previously, and the ability to robustly measure the modulus of substrate-supported coatings without specialized equipment or the need for “model systems” offered new material insights. In solvent cast coatings, the addition of 10 wt % CNCs into PVOH increased Young’s modulus from 1.6 ± 0.1 GPa (neat PVOH) to 21 ± 2 GPa. The 13-fold increase in modulus is attributed to three factors: the rigid CNCs forming a percolated network, the high compatibility between CNCs and PVOH, and the CNCs nucleating PVOH crystallites—almost doubling the matrix degree of crystallinity. Bar coating further increased Young’s modulus of the coating by 3.5-fold (compared to solvent casting), likely due to alignment of CNCs and PVOH crystallites. Higher drying temperatures and lower relative humidity also improved the CNC/PVOH coating mechanical performance; annealing increased the matrix degree of crystallinity and the modulus (ca. 6 times more for CNC/PVOH coatings than for neat PVOH), and the modulus increased by 0.4 GPa per unit decrease in relative humidity (vs 0.1 GPa for neat PVOH). Overall, CNCs can be used to tailor coating moduli over a wide range and impart higher sensitivity to processing parameters; furthermore, SIEBIMM is a facile tool to quantify mechanical properties of nanocomposite coatings prepared in different ways, such that their performance and potential applications may be fully assessed

A new quality index for benchmarking of different cellulose nanofibrils

International audienceFrom a single plant source, a wide range of mechanically-deconstructed cellulose nanomaterials can be obtained due to the large number of possible combinations of pre-treatments, mechanical disintegration process, and post-treatments. It leads to the existence of a variety of cellulose nanofibrils with different shapes, morphologies, and properties on the market. The resulting material is actually a complex mixture of nanoscale particles, microfibrillated fibers, and residual fibers on the millimeter scale. Defining a “degree of fibrillation” for determining the final cellulose nanofibril quality is a challenging issue. This study proposes a multi-criteria method to obtain the quality index of cellulose nanofibril suspensions under the form of a unique quantitative grade. According to this method, the influence of different parameters such as pulp conditioning, refining, and hemicellulose content on the defibrillation process is highlighted. This method also allows for the benchmarking of different commercial nanocellulose products